Stonycreek River Bridge (SR 403, Section 006)

Location: Somerset County, PA

Owner: Pennsylvania Department of Transportation

kantner 1Replacement of the Whistler Road Bridge over the Stonycreek River required overcoming unique environmental challenges.

CCJM initially proposed a single span P/S concrete bridge to replace the severely deteriorated and structurally deficient two-span steel I-beam structure. However, a Phase I Environmental Site Assessment (ESA) identified two significant issues of importance:

  1. A concentration of Manganese in the groundwater exceeding the applicable Act 2 Standards (statewide health standards associated with the Land Recycling Program). Additionally, the concentration of Manganese in the groundwater exceeds water quality criteria for the Stonycreek River, a trout stocked stream. This was further complicated since geotechnical investigations discovered artesian conditions.
  2. Testing of soil samples found concentrations of Cobalt and Chromium exceeding Regulated Fill Concentration Limits (RFCL) at the proposed abutment footer locations and concentrations of Cobalt exceeding Clean Fill Concentration Limits (CFCL) in the existing roadway backfill.

To reduce the potential cost associated with mitigation of these conditions, CCJM re-designed the bridge from one-span to a two-span design — nearly 60’ longer and used integral abutments on drilled piles. The roadway embankment along the southeast quadrant was steepened to 1.5:1 limiting wetland impacts and reducing fill. Although more expensive to construct than the single span, this design minimized disturbance to the existing hazardous materials reducing overall construction costs related to contaminated soil disposal and contaminated water treatment since pumped water could not be discharged into the Stonycreek River. The shallow depth of an integral abutment helped avoid any encounter with the artesian conditions found.

To mitigate the impact related to relocation of 450 feet of an adjacent small stream a replacement wetland site was incorporated in the design featuring a sinuated,  five feet  wide bench with wetland vegetation/seed mixtures, supplemental tree plantings and reuse of the existing stream bed material completed the mitigation site.